Eutectic die bonding requires heating a die solder layer or a die solder bump of a semiconductor die to a required temperature, before the semiconductor die is bonded to a substrate (e.g. a lead frame) via an interface between the heated die solder layer or bump and a substrate bond pad. The substrate is typically placed on a heated anvil to transfer heat from the heated anvil through the heat-conducting substrate to the substrate, to thereby heat the die solder layer or bump to the required temperature for eutectic die bonding.
FIG. 1 shows a conventional indexing apparatus 100 for heating a substrate 102, which comprises an array of substrate bond pads (not shown) positioned relative to a die collet 104 of a die bonder for bonding along a bonding line 106. Specifically, the indexing apparatus 100 comprises: i) an anvil 108 for supporting the substrate 102; and ii) a workholder base 110 for supporting the anvil 108. In particular, the anvil 108 is maintained at a uniform temperature (e.g. 280° C. if the die solder layer or bump is made up of a gold-tin composite) throughout the eutectic die bonding process to heat the substrate bond pads. The apparatus 100 is also configured to index the substrate 102 along direction A shown in FIG. 1, so that successive rows of the substrate bond pads are aligned with the bond line 106 to receive semiconductor dies from the die collet 104. Since the entire substrate 102 is placed on the heated anvil 108 throughout the eutectic die bonding process, a pre-bond heating time and a post-bond heating time for each substrate bond pad will thus vary depending on its location on the substrate 102. This means that the substrate bond pads that receive the semiconductor dies earlier than other substrate bond pads would have a shorter pre-bond heating time and longer post-bond heating time. This, however, increases the likelihood of internal damage of thermally vulnerable semiconductor dies, such as LED devices, during eutectic bonding.
Thus, it is an object of the present invention to seek to propose an apparatus for indexing a substrate that at least reduces the likelihood of damage to semiconductor dies during die bonding.